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Abutment pressure is one of the main sources of the complications involved as the depth of mine workings increases in the Prokop'evsk-Kiselevsk region of the Kuzbass. Its effect is to reduce the stability of the solid coal and the roads driven in the seam. Particular difficulties occur where abutment pressure zones originate from contiguous takes or where they lie on a boundary with upper levels already worked out (zones of residual abutment pressure).Planar models made from materials with scaled properties were used to study abutment pressure ahead of a face advancing in the direction of dip. These planar models simulate workings of considerable extent, for which the ends have no effect on roof deformations. Conditions of this kind will be found where a large area along the strike of a seam (e.g., a take 200-300 m in length) is being worked by a shield system, or where the pillars left between the shields are allowed to break up.The models were made on a test rig enabling us to study the effect of the surface on deformation of the strata, and the way in which the abutment pressure was formed, A 1 : 100 scale model was made of an area of solid rock 200 m deep and reaching 230 m across the strike (Fig.

period is reduced accordingly, as compared with similar parameters of vibration exciters working in a nonresonance mode.The moments of inertia incerase in proportion to the number of working pairs, with the proportional reduction of the maximum oscillation angles of pistons.An, external dissipative force reduces the effect of energy accumulation. The kinetic energy accumulated by the pistons after a certain number of oscillation cycles is transmitted to the body after reaching a certain limiting amplitude (according to the problem statement) at which the pistons strike against the body.Since the rigidity of the torsion shaft is not regulated during the course of the operation, the periodicity of collisions is constant.The asymmetric operation of the vibration exciter is based on an asymmetry of the piston oscillation angles and angular velocities.In the half-cycles, the pistons have different angular velocities, and each cycle is accompanied by a piston collision with the body in one of the directions.The vibration exciters with an elastic connection between the body and the piston create time-variable oscillation amplitudes and pulse torques: by modifying the rigidity of the torsion shaft during the course of operation, these parameters can be regulated. The vibration exciters with time-variable'vibration and shock parameters open a new potential for intensification of industrial processes.The accumulated energy of vibration exciters operating in a resonance mode, depending on the design, can be transferred partially or fully to the object treated by vibration in various industrial operations. where U is the number of fires per level and n is the serial number of the level.For example, in mines using the shield system, the number of fires per million tons of excavated coal is 1.35 on the first level and 2.35 on the third level.The incerase of the fire hazard with depth is associated with underworking and the spread of the fires that were previously considered extinguished on higher levels. These developments can be presented by using various systems of mining with a reliable insulation of horizons.Institute of Mining, Siberian Branch, Academy of Sciences of the USSR, Novosibirsk.